您的位置:首页 > 编程语言 > ASP

spring源码分析之spring注解@Aspect是如何工作的?

2019-06-03 21:57 1046 查看

AOP(Aspect Orient Programming),面向切面编程,是面向对象编程OOP的一种补充。面向对象编程是从静态角度考虑程序的结构,面向切面编程是从动态的角度考虑程序运行过程。

AOP底层,就是采用动态代理模式实现的。采用两种代理:JDK的动态代理,与CGLIB的动态代理。JDK的动态代理是面向接口的,CGLIB既可以实现有接口的,又可以实现没有接口的。(对动态代理不了解的可以看看我的其关于动态代理的介绍)

面向切面编程,就是将交叉业务逻辑封装成切面,利用AOP容器的功能将切面植入到主业务逻辑中。所谓交叉业务逻辑是指:通用的,与主业务逻辑无关的代码,如安全检查,事务日志等。

@Aspect可以使用切点函数定义切点,我们还可以使用逻辑运算符对切点进行复核运算得到复合的切点,为了在切面中重用切点,我们还可以对切点进行命名,以便在其他的地方引用定义过的切点。当一个连接点匹配多个切点时,需要考虑织入顺序的问题,此外一个重要的问题是如何再增强中访问连接点上下文的信息。

1、@Aspect

在xml定义:<aop:aspectj-autoproxy />,
其定义在http://www.springframework.org/schema/aop/spring-aop-3.0.xsd

- <xsd:element name="aspectj-autoproxy">
- <xsd:annotation>
- <xsd:documentation source="java:org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator">
- <![CDATA[
Enables the use of the @AspectJ style of Spring AOP.

]]>
</xsd:documentation>
</xsd:annotation>
- <xsd:complexType>
- <xsd:sequence>
- <xsd:element name="include" type="includeType" minOccurs="0" maxOccurs="unbounded">
- <xsd:annotation>
- <xsd:documentation>
- <![CDATA[
Indicates that only @AspectJ beans with names matched by the (regex)
pattern will be considered as defining aspects to use for Spring autoproxying.

]]>
</xsd:documentation>
</xsd:annotation>
</xsd:element>
</xsd:sequence>
- <xsd:attribute name="proxy-target-class" type="xsd:boolean" default="false">
- <xsd:annotation>
- <xsd:documentation>
- <![CDATA[
Are class-based (CGLIB) proxies to be created? By default, standard
Java interface-based proxies are created.

]]>
</xsd:documentation>
</xsd:annotation>
</xsd:attribute>
- <xsd:attribute name="expose-proxy" type="xsd:boolean" default="false">
- <xsd:annotation>
- <xsd:documentation>
- <![CDATA[
Indicate that the proxy should be exposed by the AOP framework as a
ThreadLocal for retrieval via the AopContext class. Off by default,
i.e. no guarantees that AopContext access will work.

]]>
</xsd:documentation>
</xsd:annotation>
</xsd:attribute>
</xsd:complexType>
</xsd:element>

1.1 注册

org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator
的继承关系如下:

1.2 解析过程

AspectJAutoProxyBeanDefinitionParser.java#parse()方法

public BeanDefinition parse(Element element, ParserContext parserContext) {
AopNamespaceUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(parserContext, element);
extendBeanDefinition(element, parserContext);
return null;
}

注册过程:

public static void registerAspectJAnnotationAutoProxyCreatorIfNecessary(
ParserContext parserContext, Element sourceElement) {

BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(
parserContext.getRegistry(), parserContext.extractSource(sourceElement));
useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
registerComponentIfNecessary(beanDefinition, parserContext);
}

调用实现类:

public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, Object source) {
return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);
}

1.3 具体实现类为:AbstractAutoProxyCreator的postProcessAfterInitialization()方法

DefaultAopProxyFactory#createAopProxy()方法

@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
Class<?> targetClass = config.getTargetClass();
if (targetClass == null) {
throw new AopConfigException("TargetSource cannot determine target class: " +
"Either an interface or a target is required for proxy creation.");
}
if (targetClass.isInterface()) {
return new JdkDynamicAopProxy(config);
}
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}

默认使用jdk自带的代理,还有一种cglib方式。

内容来自用户分享和网络整理,不保证内容的准确性,如有侵权内容,可联系管理员处理 点击这里给我发消息
标签: